diff --git a/src/dynamics/mpas/stepon.F90 b/src/dynamics/mpas/stepon.F90
index ab517b47..d089636e 100644
--- a/src/dynamics/mpas/stepon.F90
+++ b/src/dynamics/mpas/stepon.F90
@@ -2,11 +2,13 @@ module stepon
     ! Modules from CAM-SIMA.
     use camsrfexch, only: cam_out_t
     use dyn_comp, only: dyn_import_t, dyn_export_t, dyn_run
+    use dyn_coupling, only: dynamics_to_physics_coupling, physics_to_dynamics_coupling
     use physics_types, only: physics_state, physics_tend
     use runtime_obj, only: runtime_options
+    use time_manager, only: get_step_size
 
-    ! Modules from CESM Share.
-    use shr_kind_mod, only: kind_r8 => shr_kind_r8
+    ! Modules from CCPP.
+    use ccpp_kinds, only: kind_phys
 
     implicit none
 
@@ -27,29 +29,36 @@ end subroutine stepon_init
 
     ! Called by `cam_timestep_init` in `src/control/cam_comp.F90`.
     subroutine stepon_timestep_init(dtime_phys, cam_runtime_opts, phys_state, phys_tend, dyn_in, dyn_out)
-        real(kind_r8), intent(out) :: dtime_phys
+        real(kind_phys), intent(out) :: dtime_phys
         type(runtime_options), intent(in) :: cam_runtime_opts
-        type(physics_state), intent(inout) :: phys_state
-        type(physics_tend), intent(inout) :: phys_tend
+        type(physics_state), intent(in) :: phys_state
+        type(physics_tend), intent(in) :: phys_tend
         type(dyn_import_t), intent(in) :: dyn_in
         type(dyn_export_t), intent(in) :: dyn_out
+
+        ! Set timestep for physics.
+        dtime_phys = real(get_step_size(), kind_phys)
+
+        call dynamics_to_physics_coupling()
     end subroutine stepon_timestep_init
 
     ! Called by `cam_run2` in `src/control/cam_comp.F90`.
     subroutine stepon_run2(cam_runtime_opts, phys_state, phys_tend, dyn_in, dyn_out)
         type(runtime_options), intent(in) :: cam_runtime_opts
-        type(physics_state), intent(inout) :: phys_state
-        type(physics_tend), intent(inout) :: phys_tend
+        type(physics_state), intent(in) :: phys_state
+        type(physics_tend), intent(in) :: phys_tend
         type(dyn_import_t), intent(in) :: dyn_in
         type(dyn_export_t), intent(in) :: dyn_out
+
+        call physics_to_dynamics_coupling()
     end subroutine stepon_run2
 
     ! Called by `cam_run3` in `src/control/cam_comp.F90`.
     subroutine stepon_run3(dtime_phys, cam_runtime_opts, cam_out, phys_state, dyn_in, dyn_out)
-        real(kind_r8), intent(in) :: dtime_phys
+        real(kind_phys), intent(in) :: dtime_phys
         type(runtime_options), intent(in) :: cam_runtime_opts
-        type(cam_out_t), intent(inout) :: cam_out
-        type(physics_state), intent(inout) :: phys_state
+        type(cam_out_t), intent(in) :: cam_out
+        type(physics_state), intent(in) :: phys_state
         type(dyn_import_t), intent(in) :: dyn_in
         type(dyn_export_t), intent(in) :: dyn_out